Waste from a chemical plant, Global Chemicals, in Wales has mutated the
local insects, turning them into deadly giant monsters. With the aid of a
team of local ecologists, the Doctor and Jo set about stopping the
monsters and the environmental destruction being wrought by the refinery.
But when Mike Yates goes in undercover, he discovers that Global
Chemicals' director is not just unscrupulous: he's inhuman.

Production

Early in 1972, Doctor Who producer Barry Letts and script editor
Terrance Dicks were becoming increasingly concerned with environmental
issues. Letts had read an article about the dangers of pollution in the
magazine The Ecologist, and he and Dicks felt Doctor Who
offered them an opportunity to tell a positive message about protecting
the environment. To this end, Letts again sought the services of his
friend Robert Sloman. Sloman and Letts had cowritten The Daemons two years earlier, and Letts had
been heavily involved with Sloman's second serial, The Time Monster, the following season.

Sloman was working on a storyline for Doctor Who by October, and
The Green Death was commissioned on November 30th. As with his two
previous contributions to the series, this would be the final story of the
season. By this point, Katy Manning had suggested to Letts that she might
leave Doctor Who at the end of Season Ten. Letts consented by
January 1973: he agreed that spending longer than three years on the
programme could be injurious to Manning's career. The producer also
suspected that Jon Pertwee might be departing after the eleventh season,
and he did not want his two stars quitting Doctor Who
simultaneously. Sloman was therefore asked to amend The Green Death
to include Jo's decision to marry Cliff Jones, who would be written as a
younger version of the Doctor -- the only type of person the production
team could envision Jo leaving UNIT for.

Cliff Jones would be written as a younger version of the
Doctor: the only type of person Jo could leave UNIT for

Sloman's scripts also went through a variety of other, more minor
modifications. The chemical company was originally called Universal
Chemicals, and then United Chemicals; however, because such a business
actually existed, it was later changed to Global Chemicals. Similarly, the
character of Charles Bell was renamed Ralph Fell to avoid confusion with a
real-life chemical company executive. As well, a Nuthatch denizen
nicknamed “Face” was excised (and the relevant dialogue
assigned to Nancy instead). Wholeweal was inspired partly by Greenpeace
and partly by the Biotechnic Research And Development (BRAD) community
which had been established in Wales. It was briefly thought that Yates'
role in the latter stages of the serial might be given to Benton instead,
but this idea was not pursued. The two actors -- Richard Franklin and John
Levene -- were contracted on March 6th and 8th, respectively. Nicholas
Courtney, meanwhile, was belatedly booked to play the Brigadier on the
14th, during filming.

The director assigned to Serial TTT was Michael Briant, who had last
worked on The Sea Devils the previous year.
Amongst the suggestions made to Briant for the role of Clifford Jones was
Stewart Bevan, then Manning's real-life boyfriend. Briant was reluctant to
have Bevan audition, fearing the on-set ramifications -- especially
considering how upset Pertwee had become over the prospect of Manning's
departure -- but Bevan ultimately proved the only suitable choice for the
role.

The Welsh location schedule for The Green Death was unusually
hectic, and so Briant assembled a second unit for close-ups and
establishing shots, directed by production assistant John Harris.
Filming began on March 12th with scenes on the road and at Wholeweal;
these took place around Troed-y-Rhiw Jestyn. The second half of the day,
as well as the next three days, were occupied by scenes in and around
the mine. These were filmed at Ogilvie Colliery in Deri; the nearby
Colliery Quarry also served as Metebelis 3 on the 13th. During the Ogilvie
material, John Levene ad-libbed Benton's reference to two UNIT soldiers as
“Dicks” and “Betts” in honour of the production
team. Filming concluded with three days -- the 16th, 19th and 20th -- at
the RCA International factory at Brynmawr, which served as the Global
Chemicals building. In between, model filming took place on March
17th.

The departure of Katy Manning on April 30th marked the
beginning of the end for the “UNIT family”

Studio recording -- all of which took place in BBC Television Centre
Studio 3 -- then began with a two-day session on Monday, April 2nd and
Tuesday the 3rd for episodes one and two. Exactly two weeks later, the
majority of parts three and four were taped on the 16th and 17th; the only
exception was the material in the computer room from the fourth
installment, which was held over until the final studio block. Deviating
slightly from the Season Ten pattern, these last two days occurred on a
Sunday and Monday, April 29th and 30th. Unfortunately, Tony Adams
developed peritonitis prior to this final recording session, meaning that
he could not continue as Elgin. However, Elgin's appearances in the latter
third of The Green Death were minimal, and so he was replaced with
a new character, Mr James, played by Roy Skelton.

The departure of Katy Manning on the 30th marked the beginning of the end
for the so-called UNIT family, which had been together since the start of
Season Eight two and a half years earlier. Her decision was announced to
the public on June 22nd. Manning worked mainly in theatre after leaving
Doctor Who, and in 1982 moved to Australia with her two children.
She maintained her connection with Doctor Who, however, first by
providing the voice of erratic Time Lady Iris Wildthyme in several audio
dramas from Big Finish Productions, and then returning to Jo Grant both
for Big Finish and in 2010's Death
Of The Doctor for The Sarah Jane Adventures.

Despite the burgeoning behind-the-scenes instability, Doctor Who
had enjoyed tremendous growth during Season Ten, which came to a close
with the broadcast of The Green Death part six on June 23rd
(although the tenth recording block would continue with The Time Warrior, the first serial of Season
Eleven). The anniversary season had seen Doctor Who perform as well
in the ratings as it ever had, even returning to the Top Ten programmes of
the week during the telecast of The Three
Doctors. After years of uncertainty, Doctor Who was
enjoying renewed success, but its next big test was just around the
corner...

Sources

Doctor Who: The Handbook: The Third Doctor by David J Howe and
Stephen James Walker (1996), Virgin Publishing, ISBN 0 426 20486 7.